Generally, a manual device is applied in conventional retractable pet retractors to lock the leash spools so as to control the length of the leashes to further control the pet within a certain distance, e.g. retractable dog leashes. However, when people walk their pets, they might not pay full attention to their pets' activities. When the pets see their favorite things or when they are frightened or teased, they are likely to run around or rush into the street to hit vehicles. Some pets, such as dogs, that are likely to hurt people or damage things may rush to people or objects and cause injuries to people or damages to properties, causing economic loss to their owners or causing body harm and property loss to others.